Fault-testing articles of electrically conductive material



Jam 25, 1944.

Filed May 21 1940 ull HHHHII.

INVENTOR fiowardfi'. flames ATTORNEY Patented Jan. 25, 1944 z',s4b,150

UNITED STATES PATENT oFnce FAULT-TESTING :I;' :I CLES F ELE C- TRICALLY CONDUCTIYE MATERIAL-. I Howard E. Somes,Detroit, Mich., assignor to Budd Induction Heating, Inc., a corporation of Michigan Philadelphia, Pa.,

Application Mayzl, 1940, Serial No. 336,364

- I 3 Claims. This invention relates to the testing of elec- (ci. 73-5-1) t. high resistance sand hole or pocket such as 20 trically conductive materials for structural weaknesses and mechanical faults, and more particularly to a method of testing metallic articles for ous upon the surface thereof.

An object of this invention is to provide an improved'method of testing materials inwhich structural flaws and defects which are not obvistructural flawsand defects which are not obvisimple visual inspection. I

A further object is to provide a method of hidden from the surface by a layer of homogeneous metal such as 22, cause a bum-out resuiting from fusion at the point, thus breaking ous upon the surface 'are rendered discernible to lo testing which is equally adaptable to exterior surfaces or to the inner bores of cylinders, hubs or other annular objects;

These and other objects are accomplished by the invention hereinafter described in connection with the accompanying drawing which illustrates more or less diagrammatically one means of carrying out the present invention.

. 'face layers of the In the drawing .wherein like reference characters indicate like parts,\

Figure 1 is illustrative of a tubular member shown in section together with an apparatus for testing the same for faults, the illustration showing hidden faults and down the int al wall of the tubular object and disclosing the presence of the hidden danger, It will be appreciated that this is due to the fact that, because of 'the high frequency currents and skin eflect, the cu rtzent is urged to flow in the surface layers and a controlled depth. Consequently, if the surface layer'at any particular pointbecomes thinner than the surfacelayers present for the conduction of the high frequency currents at other points, the thinner layer will be overheated and caused to fuse and burn out. Thus, if the heating currents are caused to flow to a depth as indicated at 24 inthe 'intemal surtubular object, they will upon striking the hidden sand pocket 20 and being restricted to the thin sand holeconcealing surface layer 22 becaused to concentrate unduly and promptly fuse or burn the surface and disclose Figure 2 illustrates the same structure after testing, illustrating substantially the manner in which the faults are brought -to the internal surface so as to. be readily ascertainable by casual inspection.

Referring to the drawing, there is illustrated in Figure. 1 a cylindrical tubular object l0 arranged for test by electromagnetic induction.

For such tests an induction heating'head I2 is the existence of the dangerous sand hole immediately therebehind. This effect is illustrated in Figure'2'at 20'.

Thus it is possible by depth. .For example, if the tubular object wereonly desired to be tested to a depth equal to sub- I stantiallythe thickness of the wall 22 hiding the employed, the 'same comprisin'g a plurality of v turns ll constituting an inducing coil and a magnetic core I l cooperating therewith in order to assist in theconcentration of flux, whereby heavy currents and intense heat may be generated within the internal wall and adjoining internal layers;

of the cylinder lit. The structure of such a heat Through the use of high frequency current the ternalwall and adjacent internal layers of the tubular n'iember It being progressed uniformly along the length of the tube will, upon striking a treating head is illustrated more in detail in Patent No. 2,281,333, granted April 28, 1942,

heating is confined to the internal surface and adjoining layers, the depth of heating being onstructure of the sand hole 20, it will appear that the same would not become exposed for the reason that overheating'would not result at this point for the skin currents would be adequately carried, but if it is desired to .be assured of the' fact that the cylinder is'homogeneous to a depth exceeding that of the thickness of the wall 22 hiding thesand hole, then .by'the proper selection of speed of relative movement, frequency and power 'such'sand holes are readily exposed. The

controlling the frequency and regulating the power induced in the tube as presence of'internal'microscopic and practically invisible cracks such as 28 is also exposed by' such treatment since the same become enlarged asv illustrated in Figure 2 at28'. S "5 In order that such testing may be effected from end to end without interruption or end ect, radially laminated magnetic core end pieces SI and 32 may be applied to the-end of the tubular object-l0, thereby permitting the test tobeJ-constructure. I

It will readily appear'that the invention also show up faulty such as might-exist tinu'ed up toand including'the tip endsof the? in seam welded pipe for the reason that the faults in such seams generally are constituted by porosity and generally high resistant portions where. the seam is defective, and thus the principles above referred to would be applicable and faults thereby discovered.

Through the concentration of high frequency currents in the inner layers and to a prescribed depth whereby the tube is heated differentially,

the internal layers being heated to a desired temperature so rapidly that the outer layers are substantially unaffected, the inner layers may be caused to expand thermally and thereby stress the outer layers in tension. The diflerential'effeet may be so adjusted as to create any desired stress in the outer layers which stress would be sufficient to rupture the tube if there should be a point of weakness therein which would not stand the stress imposed.

It will be readily seen that this operation may be progressively eflected and that stress so imposed ismomentary and only exists so long as the differential heat remains, the stress gradually diminishing as the heat applied to the internal layer soaks into the outer layers. After the tube has been so treated it will be generally found to have been annealed and such residual stresses as may have been present may be considerably reduced in this way at the same time.

While such fault testing exaggerates the fault in a manner so as to render the object generally not usable, it is, of course, preferable that such defectiveobjects be discovered so that they may be discarded. .In the event that no faults are disclosed by such tests the heating and subses5 quent slow cooling in air or in such other manner as desired -will be found not to be detrimental.

There has thus. been described a simplified process of testing the walls of tubular structures 40 for adaptability to conditions wherein defects would be detrimental; for example, in internal combustion en inecylinder wall structures where wear gradually removes a certain amclmt of the metal, the presence of dangerous pockets which might be opened up by such wear is. discovered. Though the invention has been illustrated and described with reference to one application thereof, it is to be understood that the same is not limited thereto but may be practiced-in other so equivalent ways without departing from the spirit of the invention. Accordingl reference'will be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

l. The method ofvisually discerning in metallic articles capableof being heated by electromagnetic induction the presence of flaws hidden beneath the surface thereof, which consists in selecting a surface layer of predetermined depth 450 in which detrimental hidden flaws may be spaced from the article surface by metal of a thickness -less than said predetermined depth, producing visible surface indications of such flaws by electromagnetically inducing in said surface layer high-frequency, high-power heating currents of such character as to normally penetrate said layer to its full depth and in the presence of and adjacent such hidden flaws to be restricted to themetal of lesser thickness between said flaws 7 and said surface, said induced currents being sufficient to heat the metal .of lesser thickness of a thickness to a temperature sufdciently higherthan that of the adjacent flawless metal in said layer as to fuse said metal of lesser thickness and cause the same to burn out whereby to visually indicate at such surface the presence of such flaws, then cooling the metal while so controlling the cooling operation as to substantially avoid hardening or annealing effects, and then visually inspecting the article surface to discern the presence of such flaw indications.

2. The method of'vlsually discerning in annular metallic articles capable of being heated by electromagnetic induction the presence of structural flaws and defects not obvious upon the surface thereof. which'consists in producing visible surface indications of such flaws and defects y electromagnetically inducing in an inner annular surface layer of predetermined depth high-power. high frequency, electric heating currents of such character that said inner surfacelayer is caused to expand suillciently and withsuflicient rapidity to stress the surrounding relatively unheated the normal strength of said surrounding material is impaired by the presence of structural flaws and defects, then cooling the article while so controlling the cooling operation as to substantially avoid hardening or annealing effects, and then visually inspecting the article surface to discern the presence of fla'w indicating cracks.

3. The method of visually discerning in an annular metallic article capable of being heated by electromagnetic induction the presence of structural flaws and defects not obvious upon the surface thereof, which consists in producing vis ible surface indications of such flaws and defects by selecting an inner surface layer of predetermined depth in which detrimental hidden flaws may be spaced from the article surface by metal less than said predetermined depth, electromagnetically inducing in said surface layer, high-frequency, hi h-power heating currents of such character as to normally penetrate said layer to its full depth and in the pres- -ence of an adjacent to said hidden flaws to be of flawless metal and that adjacent to said flaws whereby to visually indicate at said surface the presence of such flaws, said heating currents also being of such character that said surface W is caused to expand sufficiently in extent and with sufllcientrapidity to stress the surrounding relatively unheated material to such a degree as produces visible cracks in the surface thereof at places where the normal strength of said surrounding material is impaired by the presence of structural flaws and defects, then cooling the article while so controlling the cooling operation so as to substantially avoid hardening or annealing effects, and then visually inspecting the surfaces of the article to discern the presence of such flaw indications.

HOWARD E. BONES. 

